This invention relates to an improved reforming catalyst comprising at least one noble metal and at least one alkali metal and to its use in catalytic reforming processes.
Catalytic reforming is a well known type of petroleum refinery operation which is employed to improved the octane rating of straight run gasolines. It involves converting maphtha fractions, i.e., paraffins which possess low octane ratings, to aromatics which possess high octane values. Hydrocarbon conversion reactions occurring during reforming include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of acyclic hydrocarbons to aromatics, dealkylation of alkylbenzenes, isomerization of paraffins and hydrocracking reactions which produce light gaseous hydrocarbons such as methane, ethane, propane and butanes. Hydrocracking reactions are generally undesirable and should be minimized because they decrease the yield of gasoline boiling products.
There is a high demand for high octane gasoline for use as motor fuels and the like. Accordingly, much research is dedicated to the development of improved reforming catalysts and catalytic reforming processes. Zeolite catalysts have been found to be highly useful in reforming and other naphtha upgrading processes.
Zeolite Beta, for example, has been found to be suitable for use as a catalyst for hydrocracking naphtha under mild conditions, (U.S. Pat. No. 3,923,641). However, it has been found to be desirous to further treat such catalysts by steaming to improve their activity and their stability in acid catalyzed reactions. The catalysts used in hydrocracking and/or reforming processes generally contain platinum and high acidity zeolites but have poor C.sub.4.sup.+ and C.sub.5.sup.+ selectivity (U.S. Pat. No. 4,276,151). An example of a platinum-containing reforming catalyst is described in U.S. Pat. No. 4,456,527 which relates to a reforming process having selectivity for dehydrocyclization.
It has now been found that zeolite catalysts suitable for catalytic reforming can be further improved by adding at least one alkali metal in specific controlled amounts to the zeolite so that the C.sub.5.sup.+ gasoline losses are significantly reduced and the C.sub.4.sup.+ gasoline yields are increased. The catalyts described herein are different from those described in U.S. Pat. Nos. 3,783,123 and 4,478,706 which use alkali metal containing zeolite catalyts wherein the zeolites must be specially treated and have exchangeable cations/A10.sub.2.sup.- .ltoreq.1. Furthermore, unlike alkaline earth metal zeolite catalyts which are sensitive to sulfur (U.S. Pat. No. 4,456,527), the present catalysts are stable toward sulfur containing feeds.
It is therefore, an object of this invention to provide an improved reforming catalyst and to provide a process of using said catalyst which provides significantly higher C.sub.4.sup.+ gasoline yields than conventional reforming catalyts.